Your 1999 Monaco Dynasty should not require a smog check as it probably weights over 14,000 GVWR. California requires all diesel trucks and diesel passenger cars which are 1998 model year or newer, and weight 14,000 GVWR or under, undergo a biennial smog inspection similar to their gasoline counterparts.
Follow the link below for more information regarding California Diesel Smog Check Requirements.
https://www.smogtips.com/diesel-smog-test.cfm
